A 72-year-old woman is hospitalized after an anterior ST-elevation myocardial infarction. She underwent successful percutaneous coronary intervention to the left anterior descending artery and initially improved. Her medications include aspirin, ticagrelor, atorvastatin, metoprolol, and lisinopril. On hospital day 4, she develops sudden-onset shortness of breath and profound fatigue. She denies recurrent chest pain. Temperature is 36.8°C (98.2°F), blood pressure is 86/54 mm Hg, pulse is 118/min, respiratory rate is 28/min, and oxygen saturation is 91% on room air. Physical examination demonstrates cool extremities and elevated jugular venous pressure. Cardiac auscultation reveals tachycardia and a new harsh holosystolic murmur best heard at the left lower sternal border. A palpable thrill is present over the precordium. Bibasilar crackles are noted on lung examination. ECG demonstrates persistent Q waves in leads V1-V4 without new ST-segment elevations. Troponin levels are lower than on admission. Right-heart catheterization demonstrates a significant increase in oxygen saturation between the right atrium and right ventricle.
Which of the following is the most likely explanation for this patient’s deterioration?
The correct answer is:
A) Acute rupture of the interventricular septum causing a left-to-right shunt
This patient has ventricular septal rupture (VSR), a life-threatening mechanical complication of myocardial infarction that typically occurs 2–7 days after a transmural infarction. The diagnosis is suggested by sudden hemodynamic deterioration, cardiogenic shock, a new harsh holosystolic murmur at the left sternal border, and a palpable thrill.
Myocardial necrosis weakens the interventricular septum, allowing rupture to occur several days after infarction as inflammatory degradation of tissue reaches its peak. The result is an acute left-to-right shunt, with oxygenated blood flowing from the high-pressure left ventricle into the right ventricle during systole.
The oxygen saturation “step-up” between the right atrium and right ventricle is a classic hemodynamic clue because oxygenated blood is entering the right ventricle through the septal defect. The sudden increase in pulmonary blood flow leads to pulmonary edema, while loss of forward systemic cardiac output results in hypotension and cardiogenic shock.
A high-yield Step 2 concept is distinguishing ventricular septal rupture from papillary muscle rupture. Both occur several days after MI and cause acute heart failure. However, ventricular septal rupture classically produces a harsh left sternal border murmur with a palpable thrill and evidence of a left-to-right shunt.
Definitive treatment requires urgent surgical repair.
Answer choice B: Acute rupture of the left ventricular free wall causing cardiac tamponade, is incorrect.
Free wall rupture is another catastrophic complication occurring within the first week after MI. However, it typically causes hemopericardium and cardiac tamponade, leading to hypotension, jugular venous distention, muffled heart sounds, and often pulseless electrical activity. A loud murmur and oxygen saturation step-up would not be expected.
Answer choice C: Acute rupture of the posteromedial papillary muscle causing severe mitral regurgitation, is incorrect.
Papillary muscle rupture can also occur 2–7 days after MI and causes acute pulmonary edema and shock. However, the murmur is usually best heard at the apex and radiates toward the axilla. Furthermore, there would be no oxygen saturation step-up in the right ventricle because no intracardiac shunt is present.
Answer choice D: Reinfarction due to acute coronary stent thrombosis, is incorrect.
Reinfarction generally causes recurrent ischemic chest pain, new ECG changes, and rising cardiac biomarkers. This patient’s falling troponin levels and new murmur strongly suggest a mechanical complication rather than recurrent ischemia.
Answer choice E: Ventricular aneurysm formation with mural thrombus, is incorrect.
Ventricular aneurysms typically develop weeks to months after infarction. They may cause heart failure, arrhythmias, systemic embolization, or persistent ST-segment elevation, but they do not usually cause abrupt cardiogenic shock with a new murmur several days after MI.
Key Learning Point
A patient who develops cardiogenic shock and a new harsh holosystolic murmur with a palpable thrill 2–7 days after myocardial infarction should be presumed to have ventricular septal rupture. An oxygen saturation step-up in the right ventricle is a classic diagnostic clue indicating an acute left-to-right shunt.
